Eerke Boiten has been on Facebook for six years, but studiously avoids using it on his mobile phone. The 47-year-old director of the University of Kent's cybersecurity centre only uses it on his desktop where possible; if he does access it on his mobile, it's through the browser of his Android phone. He won't use the app because he dislikes its demands to access his contacts and, more recently, his text messages: "my friends haven't given me permission to share their phone numbers, etc, with Facebook," he says. And on the desktop version he can run adblocking software.

Jason Huntley thinks similarly: the 46-year-old developer, based near Hull, is wary of Facebook on mobile because "I've heard horror stories about it corrupting your contacts, merging them with the phone's, etc. Also, I don't want Facebook to have my phone number." He has no plans to ever use the Facebook app on either his Android or iPhone, but he uses Facebook a lot because his family and friends are on it.

For Bernadette Vydra, living in Melbourne, Australia, it's quite a different story. The 36-year-old mother of two used to use Facebook on her PC; now, though, she only ever uses it on her iPhone (and occasionally iPad). "With an infant and a toddler, it's the quickest way and smallest device (to keep away from little baby fingers)," she explains. The other reason for using Facebook on mobile, she says, is that "when I am working, corporate networks tend to block sites like Facebook."

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Danny Denhard, 31, based in London, also only uses Facebook on mobile now, despite having been a user since it opened up beyond academia. "The desktop is too busy and even noisy," he says. "Customising my experience on mobile is far easier and better than on desktop." As a digital marketing professional, he says he's noticed that family and friends find the desktop experience "increasingly difficult and misleading" - what's an ad, what's a sponsored story?

Facebook's own figures show that the trend is in the direction of people like Vydra and Denhard - whose busier lives mean that Facebook use has to be squeezed into smaller segments. According to the company's most recent financial results, it had a total of 1,230 million users during the month of December 2013; of those, 296 million accessed the site only through their mobile, and 285 million only via the desktop. That of course leaves the majority, 649 million, accessing it through a mixture - sometimes on desktop, sometimes on mobile.

But it's the trend that's most telling. Facebook's numbers show desktop-only users (whose number can be calculated by taking the total monthly users, and subtracting the "mobile" users - which includes both mobile-only and mobile-and-desktop users) are a dwindling band.

At the end of 2012, they were 376 million of the 1,056 million total (or 35%); now they are 285 million of 1,230 million (23%). The shift has been coming for a long time: at the end of 2012, Facebook said that in December 2012 "mobile daily active users exceeded web daily active users for the first time". But it's taken a while for that to become embedded enough for mobile-only to overcome desktop-only.

Why? While it's far from scientific, when I sought (via Twitter) people who exclusively use Facebook on the desktop (or laptop), or exclusively on mobile, it was the latter who were more plentiful. Besides Vydra, another new parent told me that while he previously used the site on desktop, he now didn't have the time; mobile-only was the solution.

Better security on mobiles and tablets

Another, Sean Cansdale, explained that he has used the desktop version perhaps a couple of times in a year: "a good thing about keeping it exclusive to mobile/tablet is security, as it is far easier for me to secure my device than my home/work computer."

What's important is that Facebook has managed to keep up with that trend. For many companies which started their lives in the "desktop era" - arguably up to about 2009, when the last of the "big desktop" apps appeared (Spotify and Dropbox) - the key problem has been how to shift to the rapidly-growing mobile space, which is where the biggest new opportunity lies.

That's no surprise, says Denhard: "Facebook mobile has become one of the main destinations for second-screen experiences [when people watch TV and talk about it on social media] and [I] expect that to continue with public hashtag statuses," he remarks.

Perhaps it's telling that both the desktop-only users, Boiten and Huntley, are security-minded; it was Huntley who discovered that LG's Smart TV was sending back data about what you watched to LG servers. Boiten says he would consider using it on his Android phone if he could control the permissions for what data Facebook can access; at the moment it's all or nothing. For Facebook, though, more data is always helpful in targeting ads - and mobiles do tend to give away more information, including location, and contact and email data.

Mobile growth was powered by smartphones

Facebook started on the desktop 10 years ago; mobile use only began to take off once capable smartphones were around. It launched an iPhone website in August 2007 to grab those very early adopters, and then in July 2008 launched its iPhone app. Its Android app had to wait a long time - until 2010 - but the rise of Android phones has meant more priority being given to it.

The shift to mobile has posed problems for Facebook though. As a site born in the days of desktop-only, it had to adjust quickly to a world where people were accessing the web just as much, or more, online - and where, as those parents' experience shows, they were going through life stages which completely altered their relationship with computing.

The first big step was Zuckerberg's decision to drop HTML5 in August 2012, and instead write "native" apps for each platform, specifically to be able to benefit from greater processing speed, despite the extra coding involved.

Some of those attempts have flopped - look at Facebook Home, which aimed to be a "launcher" that would in effect take over Android phones, and put your Facebook friends front and centre. Launched in April 2013, it was built into the HTC First - a phone that sold embarrassingly poorly, and quickly discontinued in the US due to customer indifference (and never launched in Europe).

Facebook Home seemed to be a step too far; people didn't want their phone to be inside Facebook, they wanted Facebook in their phone. Despite an update in December, Home is still poorly rated on Google Play, and has been downloaded fewer than 5m times, despite a potential install base many times larger.

Zuckerberg and his team reacted to that failure by splitting Facebook's mobile shape into different pieces: a Poke app, a Chat app, effectively splintering Facebook into separate "app pieces" on mobile so that it could be sure of being used at some point. That worked for Vydra, who often uses text messages to communicate with other mothers: "I have found that chat on FB to be quite handy for communicating with other mums too The group conversation is good for keeping up with people."

The key to mobile success though has been in making money from adverts on mobile - a trick that even Google (with its roots far deeper on the desktop) seems to struggle with.

In its most recent financial results, Facebook said that 53% of its $2.34bn advertising revenue came from mobile users - compared to just 23% a year ago. It's that transformation which really suggests that Facebook has successfully mastered the shift to mobile.

In actual numbers, desktop revenue is essentially flat; it's mobile advertising that has taken off. Facebook, after a years-long runup, has finally begun flying free of the desktop.

With mobile set to grow and grow, that means that its future as a money-maker - and as the social network people use - is assured. In ten years' time, desktop-only users might be only a tiny part of its total users - and its revenue generation.